This application is related to application Ser. No. 648,460, filed Jan. 12, 1976, which is hereby incorporated by reference in its entirety. This invention relates to an emergency dead stop step chucking assembly for conventional collets, which assembly is configured to be utilized without the need for a specially designed collet. The assembly of the invention is particularly appropriate for use in the handling of workpieces of short length. Moreover, the arrangement of the invention is such that variations in the diameter of the part will not affect the positive end length control of the workpiece. The chucking assembly of the invention is comprised of a soft metal which may be easily machined to fit any part diameter up to, for example, two inches for a standard one inch 5C collet, with 0.75 inch chucking length, while still preventing workpiece drawback on the closing of the collet.
This is achieved by providing a step chuck with an enlarged forward portion, with a shank extending from the rear face thereof which fits into the bore of a conventional collet. The assembly includes a spring collar which is inserted into the rear end of the collet bore, which spring collar is held in place with a spring biased shoulder screw. Thus, the collet front face is spring biased against the rear face of the enlarged forward portion of the chuck body. In this connection, the rear face of the collet body includes an annular recess for receiving the front end of the collet.
The rearwardly extending shank of the chuck body includes a radially extending orienting pin, which cooperates in sliding engagement with one of the circumferentially spaced longitudinally extending slots in the collet to prevent relative rotation between the chuck body and the collet. Also included herewith is a circumferential reminder "groove" on the enlarged chuck body to delineate the maximum depth allowable for boring to receive the workpiece in the chuck.
The rearwardly extending shank portion of the chuck body includes an axial bore, which is threaded near the rear end thereof to receive the shoulder screw of the holdback spring of the assembly. Moreover, this bore extends forwardly through the entire shank and into the enlarged forward body of the chuck. It thus serves as an access for minor machining of the radially innermost portions of the jaws of the chuck body at the intersecting points thereof in order to provide a small bore extending through the chuck body up to the point of the reminder groove. By providing this bore, a resilient plug may be inserted through the bore up to the point of the reminder groove. This resilient plug serves to impart to the chuck assembly of the invention a spring tempered property not ordinarily existing in emergency chucking assemblies comprised of soft metal. This "spring temper effect" enhances the gripping action of the chuck as the jaws thereof collapse around a workpiece inserted into the bore machined or turned into the chuck body for receiving the workpiece.
Thus, when the assembly of the invention is made up on a conventional collet and connected to a drawtube, the closer may be activated to hold the spacer pins tightly positioned in longitudinally extending slots of the chuck body. Then, the front face thereof may be turned or bored to the largest part diameter allowed by tolerances on the part diameter and the release closer activated to release pressure on the spacer pins. Subsequently, after the spacer pins are removed and any cleaning of the prepared bore completed, the chucking assembly of the invention is ready for receiving the workpiece.
With the foregoing objects in view, this invention will now be described in more detail, and other objects and advantages thereof will be apparent from the following description, the accompanying drawings, and the appended claims.